Correlation of optical absorption and density of paramagnetic centers in a-C : H films

15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides, and Silicon Carbide, Riva del Garda, ITALY, SEP 12-17, 2004International audienceWe investigated a-C:H films deposited by dual electron cyclotron resonance radio frequency plasma-enhanced chemical vapour deposition (PECVD) by optical absorption and electron spin resonance (ESR) spectroscopy. We show that the variation of the density of paramagnetic centers obtained from ESR spectroscopy can be directly correlated to the low energy part of the optical absorption spectrum revealed by photothermal deflection spectroscopy (PDS). A simple analysis of the low energy part of the optical absorption spectrum is proposed, which allows an assessment of the density of states at the Fermi level. We interpret this result in terms of intraband transitions of localized defects situated far from the pi-pi* band tails, which dominate the higher energy part of the optical absorption spectrum. (c) 2004 Elsevier B.V. All Rights Reserved

Structural and optical properties of Pb2KNb5O15 and GdK2Nb5O15 tungsten bronze thin films grown by pulsed laser deposition

International audienceLead potassium niobate Pb2KNb5O15 (PKN) and gadolinium potassium niobate GdK2Nb5O15 (GKN) thin films were grown on (001) MgO single crystal substrates using pulsed laser deposition technique. PKN and GKN thin films were characterized by X-ray diffraction and their linear optical properties were determined. The out-of-plane orientation of PKN thin film depends on the oxygen pressure used during the growth process: [001] for low pressure and [530] for high pressure. In contrast, GKN thin film is oriented [001] and is less sensitive to pressure. PKN and GKN thin films were found transparent and their refractive index quite similar to that reported on TTB-type ferroelectric oxides. GKN film exhibits high bandgap compared to the PKN film. (C) 2017 Elsevier B.V. All rights reserved

Modes of Hydrogen Incorporation in Hydrogenated Amorphous Carbon (a–C:H), Modifications with Annealing Temperature

In order to obtain more information about the nature of the hydrogen bonding and the thermal stability of a-C:H films, we have studied two different types of films labeled I and II deposited in a d.c. multipolar plasma system from pure methane at substrate bias equal to $-40$ and $-600$ V respectively. A combination of several complementary techniques has been carried out on the samples in their as-deposited state as well as after isochronal annealing cycles at increasing temperatures up to 650 $^{\circ}$C. The results clearly indicate that the two types of samples have very different H bonding and microstructure in their as-deposited state. They also behave differently upon annealing and still exhibit quite different microstructures and H bonding configurations up to high annealing temperature

Optical, electrical and magnetic properties of transparent, n-type conductive Zn0.90-x,V0.10AlxO thin films elaborated from aerogel nanoparticles

International audienceVanadium-aluminium co-doped ZnO thin films have been grown by rf-magnetron sputtering of Zn0.90-xV0.10AlxO (x = 0.01 to 0.03) aerogel nanoparticles. Even though the films were deposited at room temperature they were of good crystal quality and showed c-axis texturing normal to the film surface. The films are highly transparent in the visible with a transmittance higher than 90%. The highest conductivity of 5.10(3) Omega(-1) cm(-1) is obtained for 1% Al doping. The incorporation of V, a notoriously difficult dopant in ZnO, is confirmed by the observation of different absorption bands near 800 nm which we attribute to intracenter transitions of Zn substituted V2+. The magnetic properties of the aerogel particles have been studied by electron paramagnetic resonance (EPR) spectroscopy. No evidence for a ferromagnetic phase is found contrary to theoretical predictions. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Effect of CdSe nanoparticles incorporation on the performance of P3OT organic photovoltaic cells

International audiencePhotoluminescence and photovoltaic properties of P3OT:%CdSe nanocomposite films are investigated as a function of the mass concentration (wt%) of the CdSe nanoparticles (NPs) incorporated in the films. The incorporation of CdSe NPs produces a quenching of the photoluminescence and improves the performance of the nanocomposite solar cells. These effects are explained in terms of exciton dissociation and charge separation occurring at P3OT/CdSe interfaces within the Forster formalism, involving non-radiative energy transfer from the donor (P3OT) to the acceptor (CdSe NPs). An exciton quenching rate constant of 1.4 x 10(-10) cm(3) s(-1) is determined using the Stern-Volmer equation. In addition, scanning electron microscopy (SEM) images reveal that surface morphology is changed by CdSe NPs incorporation, in agreement with FTIR spectra. The current density-voltage (I-V) characteristics of ITO/P3OT:%CdSe/Al photovoltaic cells performed for different CdSe concentrations are also reported and indicate a significant improvement of the photovoltaic parameters cells, particularly, the conversion efficiency becomes 20 times greater than that of the cell based on pure polymer. (C) 2015 Elsevier Ltd. All rights reserved

Structural and magnetic properties of Co-doped ZnO thin films grown by ultrasonic spray pyrolysis method

International audienceCobalt-doped ZnO thin films with several different percentage of Co from 0 up to 15 at% were synthesized via a cheap, simple and versatile method i.e. ultrasonic spray pyrolysis at atmospheric pressure and a substrate temperature of 350 degrees C. The structure of the as prepared samples was characterized by X-ray diffraction (XRD), Raman spectroscopy and FTIR. The Co-doping effect is revealed by the presence of three additional peaks around 235, 470 and 538 cm(-1) respect to the Raman spectra of the unsubstituted film. Fourier transform infrared spectroscopy (FTIR) put in evidence the decrease of the bond force constant f with increasing Co-doping. By ultra-violet visible near infrared (UV-Vis-NIR) spectroscopy on Co-doped samples it was possible to show the presence of additional absorption bands at approximately 570, 620 and 660 nm suggesting that Co2+ ions do not change their oxidation when substituted to zinc and the ZnO lattice does not change its wurtzite structure as well. Finally, all our samples exhibit a paramagnetic behavior without any trace of intrinsic room temperature ferromagnetism. (C) 2016 Elsevier Ltd. All rights reserved

Hydrogenated amorphous carbon film coating of PET bottles for gas diffusion barriers

16th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, and Nitrides, Toulouse, FRANCE, SEP 11-16, 2005International audienceThe addition of a gas-impermeable coating on the inside wall of a standard polyethylene tereplithalate (PET) bottle has long been considered as a way to improve the packaging for beer, juice and carbonated soft drinks. We have developed a plasma-assisted deposition process suitable for the deposition of 100 nm thick, transparent, hydrogenated amorphous carbon (a-C:H) films on PET surfaces. The Sidel plasma technology uses an acetylene gas precursor and a microwave plasma, which allows us to obtain a high deposition rate of 60 nm/s necessary for industrial process flows. The a-C:H films provide a 50-fold reduction of the permeation rates Of O-2 . The composition, optical, structural and defect properties of the a-C:H films were characterized by Rutherford Back Scattering (RBS), Elastic Recoil Detection Analysis (ERDA), X-ray Photoelectron Spectroscopy (XPS), optical spectroscopy, Raman and Electron Paramagnetic Resonance (EPR). (c) 2005 Elsevier B.V. All rights reserved

Effect of the KOH chemical treatment on the optical and photocatalytic properties of BiVO4 thin films

International audienceIn this work, we present the structural, optical and photocatalytic properties of BiVO4 thin films produced by a dual-magnetron sputtering process using both Bi2O3 (alpha-phase, 99.98 % purity) and V (99.9 % purity) targets under Ar/O-2 atmosphere with a ratio of 18:2. The films were deposited varying the power applied to the targets to obtain stoichiometric films, and the monoclinic structure was achieved by post-deposition annealing. The dual process was chosen to better control the Bi/V ratio since Bi and V have very different sputtering yields. In particular, the influence of a chemical treatment using potassium hydroxide (KOH) on the optical properties and different dye discolorations (acid blue 113 and methyl orange) is discussed. The optical properties were studied by reflectance and transmittance spectroscopy, where the spectra were fitted to obtain the refractive index dispersion and the optical band gap of the BiVO4 as a function of the film structure, as determined by X-ray diffraction and Raman spectroscopy